Spark plug



c. G. ERNY 2,064,738

SPARK PLUG Filed Nov. 8, 1935 fru erafora- Patented Dec. 15, 1936 UNITED STATES ArENr OFFICE 7 Claims.

This invention relates to improvements in spark plugs of the general type disclosed in my U. S. Patent No. 1,983,445, dated December 4, 1934, and the object of the present invention is to improve the prior construction in certain respects hereinafter set forth and to provide a spark plug that shall be characterized by compactness of form and a generally improved operating efficiency.

In the attached drawing:

Figure 1 is an elevational and partial sectional view illustrating a plug made in accordance with the present invention;

Fig. 2 is an inverted plan view of the plug;

Fig. 3 is a section on the line 3-3, Fig. l, and

Fig. 4 is a fragmentary sectional View showing a modification within the scope of the invention.

With reference to the drawing, the plug comprises the usual body or casing member I within which is confined in conventional manner, as by means of a gland 2 threaded into the body, the usual insulator 3. The insulator 3 in accordance with the usual practice contains an electrode 4 which projects into the firing chamber of the plug and which extends longitudinally through the insulator 3 to the outer end thereof where it is exposed for connection to the source of electrical energy. The plug further comprises a second electrode 5 which with the electrode 4 forms the usual spark gap, this electrode 5 being supported in the metallic casing l and being grounded through the motor in which the plug is mounted. In the foregoing general respects the plug conforms to the conventional practice.

In accordance with the present invention, the casing l at the firing end of the plug terminates in a relatively shallow extension 6 of greatly reduced diameter adjacent the bottom of which the grounded electrode 5 is located. The walls of this extension 6 are relatively thin, while the wall thickness of that portion of the casing adjoining the base of the extension 6 and from which the extension projects is relatively great. This relatively thick portion of the casing is threaded, and in assembly with a motor is in direct contact with the cooled portions of the motor body. The insulator 3 preferably terminates short of the inner end of the extension 6, and the electrode 4 projects from the end of the insulator into the chamber of the extension 6 and into proximity with the grounded electrode 5. Propagation of the explosion, therefore, occurs within the relatively restricted space embraced by the extension 6.

As shown in Figs. 3 and 4, the side wall of the extension 6 is provided with three uniformly spaced firing ports 1, these ports preferably being of as great diameter as possible, and one of the ports as shown in Figs. 1 and 3 is aligned with and lies directly opposite the free end of the electrode 5, the other end of the electrode being fixed in the wall of the extension. The extension 6 is also provided in the bottom with a relatively small centrally positioned port 8, the function of which will be hereinafter set forth.

In accordance with a principle of my prior invention as set forth in the aforesaid U. S. Patent No. 1,983,445, I provide a plurality of ports 9 extending inwardly from the surface of the casing l adjoining the base of the projection 6 to a point adjacent the inner end of the firing chamber, the outer end of which is terminated by the flamepropagating chamber in the extension 6. These ports function to ventilate or scavenge the spent gases from the firing chamber.

The aforedescribed construction combines extreme compactness of form with high functional efii'ciency. This is due in part to the fact that the explosive flame as previously set forth is propagated in a relatively restricted chamber having large ports for access to the chamber of the explosive mixture and through which the flame may be efficiently projected into the cylinder chamber in a plurality of directions from the propagating center. At the same time, the ventilating ports 9 insure a highly efficient scavenging from the combustion chamber of the spent gases and prepare the chamber for reception of a fresh supply of explosive mixture after each firing. The small aperture 8 in the end of the extension 6 hasbeen found to materially aid the efiicient operation of the spark plug when the motor is idling, and is so relatively small as to effectively exclude free access to the firing chamber from the inner end of the plug of oils and substances which might tend to foul the electrodes.

Another valuable feature of the invention resides in the location of the grounded electrode 5 in alignment with one of the firing ports I, in that it affords ready access through said port to the free end of the electrode for adjustment of the spark gap, and permits accurate measurement of the gap by means of a suitable instrument.

It will be noted that the extension 6 constitutes the only portion of the plug projecting into the engine cylinder, and that the relatively thick walled portion immediately adjoining the base of the extension 6 is in close heat conductive contact with the cooled portion of the engine block. I have found that by regulating the thickness of this latter portion of the plug casing and the cross sectional area of the juncture between this portion and the extension 6, the operating temperature of the plug may be accurately controlled. Thus in the embodiment of my invention shown in Fig. 1, it will be noted that the casing l is so formed in the interior as to provide in the threaded portion thereof a relatively thin wall as compared for example with the embodiment shown in Fig. l, and that also in the plug illustrated in Fig. l, the mass of metal connecting the threaded portion of the casing with the extension 6 is relatively small. The plug shown in Fig. 1, therefore, will operate at relatively high temperatures as compared with that disclosed in Fig. 4, this by reason in the latter case of the increased mass of metal adjoining the base of the extension 6 and connecting the extension with the cooling source. By this slight modification in the structure of the plug involving no essential change nor increased expense in the general process of manufacture, the plugs may be made to conform to the characteristics of diiferent motors.

I claim:

1. A spark plug comprising a casing having toward one end an externally threaded portion constituting a means for securing the plug in the wall of an engine cylinder, a casing extension of greatly reduced diameter projecting axially from the end of said threaded portion and having an outer end wall defining the terminal end of a firing chamber within the casing, said extension having in the side thereof an opening constituting a firing port, an insulator secured in the casing and forming an inner wall of said chamber, a sparking terminal secured at one end thereof in the side wall of said extension and having its free end extending in proximity to and substantially in alignment with said firing port, and a second terminal mounted in the insulator and projecting into the interior of said extension in proximity to the terminal first named, said extension providing a flame-propagating chamber of small area terminating the firing chamber and housing the spark gap.

2. A spark plug comprising a casing having toward one end an externally threaded portion constituting a means for securing the plug in the wall of an engine cylinder, a casing extension of greatly reduced diameter projecting axially from the end of said threaded portion and having an outer end wall defining the terminal end of a. firing chamber within the casing, said extension having in the side thereof an opening constituting a firing port and having an opening in said end wall, an insulator secured in the casing and forming an inner wall of said chamber, a sparking terminal secured in said extension, and a second terminal mounted in the insulator and projecting into the interior of said extension in proximity to the terminal first named, said extension providing a flame-propagating chamber of small area terminating the firing chamber and housing the spark gap.

3. A spark plug comprising a casing having toward one end an externally threaded portion constituting a means for securing the plug in the wall of an engine cylinder, a casing extension of greatly reduced diameter projecting axially from the end of said threaded portion and forming the outer terminal end of a firing chamber within the casing, said extension having an opening constituting a firing port, an insulator secured in the casing and forming an inner wall of said chamber, a sparking terminal secured in said extension, and a second terminal mounted in the insulator and projecting into the interior of said extension in proximity to the terminal first named to form the spark gap, said extension providing a flamepropagating chamber of small area terminating the outer end of the firing chamber and housing said gap, and said casing having a. port extending through the said threaded portion thereof from a point adjacent the inner end of the firing chamber to the outer end of said threaded portion at a point radially removed from the base of said extension.

4. A spark plug comprising a casing having toward one end an externally threaded portion constituting a means .10? securing the plug in the wall of an engine cylinder, a casing extension of greatly reduced diameter projecting axially from the end of said threaded portion and forming the outer terminal end of a firing chamber within the casing, said extension having in the sides thereof a plurality of openings constituting firing ports, an insulator secured in the casing and forming an inner Wall of said chamber, a sparking terminal secured in said extension, and a second terminal mounted in the insulator and projecting into the interior of said extension in proximity to the terminal first named to form the spark gap, said extension providing a flame-propagating chamber of small area terminating the outer end of the firing chamber and housing said gap, and said casing having in the said threaded portion thereof a plurality of ports extending from points adjacent the inner end of said firing chamber to points at the outer end of said threaded portion radially removed from the base of said extension.

5. A spark plug comprising a casing having toward one end an externally threaded portion constituting a means for securing the plug in the wall of an engine cylinder, a casing extension of greatly reduced diameter projecting axially from the end of said threaded portion and having an outer end wall defining the terminal end of a firing chamber within the casing, said extension having an aperture in said end wall and having in the sides thereof a plurality of openings constituting firing ports, an insulator secured in the casing and forming an inner wall of said chamber, a sparking terminal secured in said extension, and a second terminal mounted in the insulator and projecting into the interior of said extension in proximity to the terminal first named to form the spark gap, said extension providing a flame-propagating chamber of small area terminating the firing chamber and housing the spark gap, and said casing having in the said threaded portion thereof a plurality of ports extending from points adjacent the inner end of said firing chamber to points at the outer end of said threaded portion radially removed from the base of said extension.

6. A spark plug comprising a casing having toward one end an externally threaded portion constituting a means for securing the plug in the wall of an engine cylinder, a casing extension of greatly reduced diameter projecting axially from the end of said threaded portion and forming the outer terminal end of a firing chamber within the casing, said extension having an opening constituting a firing port and being materially smaller in cross sectional area than the inner end of said firing chamber, an insulator secured in the casing and forming aninner wall of said chamber, said insulator having a tapered end portion extending into said chamber from the inner end, and the inner wall surface of said threaded portion of the casing being correspondingly tapered and lying in proximity to the said tapered end of the insulator, a sparking terminal secured in said extension, and a second terminal mounted in the insulator and projecting into the interior of said extension and in proximity to the terminal first named to form the spark gap, said extension providing a flame-propagating chamber of small area terminating the firing chamber and housing said gap.

'7. A spark plug comprising a casing having toward one end an externally threaded portion constituting a means for securing the plug in the wall of an engine cylinder, a casing extension of greatly reduced diameter projecting axially from the end of said threaded portion and forming the outer terminal end of a firing chamber within the casing, said extension having an opening con stituting a firing port, an insulator secured in the casing and forming an inner Wall of said chamher and having a tapered end portion projecting into the firing chamber from the inner end thereof, the surface of said tapered portion of the insulator diverging from the inner wall surface of the firing chamber and being relatively remote thereto, a sparking terminal secured in said extension, and a. second terminal mounted in the insulator and projecting into the interior of said extension in proximity to the terminal first named to form the spark gap, said extension providing a flame-propagating chamber of small area terminating the firing chamber and housing said gap.

CHARLES G. ERNY. 

